The present invention relates to a system and a method for improved utilization of available frequency bandwidth in a wireless communication system with asymmetrical traffic load. The invention also relates to devices that are intended to be incorporated in such a system.
In traditional communication systems for wireless communication between two or more devices, there are often equally large frequency ranges reserved for transmission and for reception in each device. Examples are systems with so-called frequency duplex, in other words systems in which the incorporated devices can transmit and receive simultaneously at two different frequency ranges. An example of such a system is the so-called NMT system. In such a system, each device transmits on one of its frequency ranges and receives on the other, and when two devices are communicating with each other it is the case that the transmission range of one device corresponds to the reception range of the other device, and vice versa.
For the transmission of speech, in principle equally large amounts of information are transmitted in both directions, which means that each device utilizes its allocated frequency range to an equally large extent. When the amount of data traffic increases in such systems, however, an imbalance arises in the utilization of the allocated bandwidth, as then it can often be the case that one of the communicating devices transmits considerably more than it receives, while the other device consequently receives considerably more than it transmits.
The bandwidth that is reserved in order for the receiving device to be able to transmit (and in order for the transmitting device to be able to receive) is consequently poorly utilized, while at the same time the transmission of the amounts of data involved takes a relatively long time.
A method for achieving improved utilization of available bandwidth in a system with asymmetrical transmission requirements is to utilize so-called time-division or time multiplexing, which means that the devices transmit on the same frequency at different times and for as long a time as is required in order for the information to be transmitted. A disadvantage of this solution is that the frequency duplex capability is lost. A further disadvantage of this type of solution is that the frequency-allocating authorities often require reception to take place on one frequency range and transmission on another, which requirement cannot be met in purely time-multiplexed systems.
There is thus a need to be able to utilize bandwidth reserved for transmission and reception in a device in a wireless communication system on occasions when the device does not require the bandwidth that has been reserved for reception or transmission, while at the same time retaining the frequency duplex capability.
This need is solved according to the present invention by means of a first communication device intended for communication with a second communication device, which first device is provided with means for simultaneously transmitting on a first frequency and receiving on a second frequency. Based on the need of the respective devices to transmit information within a particular interval of time, the first device is provided with means for dividing up the said interval of time into a number of sub-intervals in conjunction with corresponding means in the second device, the first unit being provided with means for simultaneously transmitting on both the first and the second frequencies.
The invention also comprises a first communication device for communication with a second communication device, which first device is provided with means for simultaneously transmitting on a first frequency and receiving on a second frequency, which first device, based on the need of the respective devices to transmit information to the other device within a particular interval of time, is provided with means for dividing up the said interval of time into a number of sub-intervals in conjunction with corresponding means in the second device, the first device being provided with means for simultaneously receiving on both the first and the second frequencies.
This provides a very high level of flexibility, as one and the same device can utilize its allocated bandwidth adaptively as required, either for simultaneously transmitting and receiving, or only transmitting, or only receiving, according to the actual requirement.
A further advantage of a device according to the invention is that it can be used together with devices that transmit and receive simultaneously and also with equipment that transmits and receives alternatively. This means that a device according to the invention can be used together with equipment from existing systems and also with equipment in accordance with future systems, while at the same time older types of equipment can be incorporated into systems that mainly comprise devices according to the invention.
The devices according to the invention can advantageously be combined to create a communication system comprising a first and a second communication device intended for transmitting information to each other, where each device comprises means for simultaneously transmitting on a first frequency and receiving on a second frequency, the first and the second devices, based on the need of the respective devices to transmit information within a particular interval of time, both being provided with means for dividing up the said interval of time into a number of sub-intervals in conjunction with each other, the first device comprising means for simultaneously transmitting on both the first and the second frequencies within a number of the said sub-intervals and the second device comprising means for simultaneously receiving on both the first and the second frequencies within these sub-intervals.